Integrated semiconductor diode

Abstract: A diode integrated on semiconductor material with BCD technology and of the type provided on a bulk (2) having a first type of conductivity inside a retention region (8) having a second type of conductivity. The diode comprises also a buried anode region (4) having a first type of conductivity and a cathode region (12) having a second type of conductivity. Said cathode region (12) comprises an epitaxial layer (6) located above the buried anode region (4) and a high dope region (11) provided inside the epitaxial layer (6). The buried anode region (4) comprises depressions (5) opposite which is located the high dope region (11) with said depressions (5) being achieved by the intersection of lateral diffusions of distinct and adjacent portions of the buried anode region (4).

Description: The present invention relates to a semiconductor diode and specifically to low leakage semiconductor diodes integrated with BCD technology. In accordance with the known art a low leakage diode structure comprises a diffused anode region on which is provided a cathode region comprising a type N epitaxial layer with high resistivity and a type N high dope region. As known, the breakdown voltage of the junction of a low leakage diode depends on the characteristics of the epitaxial layer and in particular on the thickness of the epitaxial layer portion between the high dope cathode region and the underlying diffused anode region. More precisely, this value depends upon the distance between these two regions. The breakdown voltage depends also on the resistivity of the epitaxial layer. To increase this value without changing the diode manufacturing process phases with resulting cost increase, it is necessary to act upon the thickness and/or resistivity of the epitaxial layer. But these characteristics are generally fixed in such a manner as to optimise the performance of the power components which, with integrated circuits achieved with BCD technology, are represented by DMOS transistors. The technical problem underlying the present invention is to provide a semiconductor diode integrated with BCD technology having high breakdown voltage of the junction without changing the manufacturing process phases nor the characteristics of the epitaxial layer. The solution idea underlying the present invention is to provide a diode structure in which the distance between the diffused anode region and the high dope cathode region is increased without changing the diode manufacturing process nor the thickness and/or resistivity of the epitaxial layer. The technical problem is solved by a semiconductor integrated diode as defined in claim 1. The characteristics and advantages of the circuit in accordance with the present invention are set forth in the description of an embodiment thereof given below by way of nonlimiting example with reference to the annexed drawings. In the drawings - FIG. 1 shows a diagram in enlarged scale and vertical cross section of a semiconductor diode provided in accordance with the present invention, and FIG. 2 shows a top view of the diode of FIG. 1. With reference to the figures reference number 1 indicates as a whole and schematically a semiconductor diode provided in accordance with the present invention. For convenience of discussion the structure of the diode 1 in accordance with the present invention is now described with reference to the process phases which lead to its realisation. For the manufacture of the diode there is used a bulk 2 of semiconductor material, e.g. silicon, having a first type of conductivity and specifically type P. On the bulk 2 is provided by antimony ion implantation and subsequent diffusion heat treatment a first buried region 3 having a second type of conductivity and specifically type N. Subsequently, on this first buried region 3 is provided by boron ion implantation a second buried region 4 with anode function and having the first type of conductivity. For the formation of the second buried region 4 there is used a mask with appropriate windows so as to achieve boron ion implantation concentrated in distinct and regularly spaced portions overlying the buried first region 3. In this manner, by successive diffusion heat treatments, by utilising the lateral diffusion of the distinct anode portions, the second buried region 4 takes on a configuration with multiple depressions 5 achieved each by the intersection of the lateral diffusions of adjacent distinct portions. The manufacturing process of the diode 1 continues with the growth of an epitaxial layer 6 having the second type of conductivity. In the epitaxial layer 6 is then performed a phosphorous ion implantation which by subsequent diffusion will originate a first deep annular region 7 having the second type of conductivity in contact with the buried first region 3. This diffusion allows formation of a retention region 8 designed to inhibit turning on of a PNP parasite transistor present towards the insulation. Inside a portion 9 of epitaxial layer 6 included in the first deep annular region 7 is provided by boron ion implantation and subsequent diffusion heat treatment a second deep annular region 10 with anode function and having a first type of conductivity and in contact with the second buried region 4. Again inside the portion 9 of epitaxial layer 6 by arsenic ion implantation and subsequent diffusion heat treatment there is achieved a high dope region 11 having the second type of conductivity. At the end of the manufacturing process of the diode 1 the cathode region 12 is formed from the portion 9 of epitaxial layer included in the deep annular region 10 and from the high dope region 11. Specifically the high dope region 11 comprises at least two structurally independent regions 13, 14 located opposite the depressions 5 of the second buried region 4. Advantageously thanks to this particular conformation of the diode 1 the distance between the second buried region 4 and the high dope region 11 and consequently the breakdown voltage of the junction of diode 1 is increased. In addition this result was achieved without changing the manufacturing process of the diode nor the characteristics of the epitaxial layer 6. Furthermore, having moved the high dope region 11 away from the second buried region 4, impurities having the first type of conductivity are prevented from spreading in the high dope region 11 during diffusion of the second buried region 4. In this manner the diode current leakage value is further lowered. In addition, the second buried region 4 being formed by the intersection of adjacent lateral diffusions, this region has lower doping and hence originates less crystallographic defects in the epitaxial layer 6.

Claims: Diode integrated on a semiconductor bulk (2) of a first type of conductivity having a retention region (8) of a second type of conductivity formed in said bulk (2) and comprising a buried anode region (4) of the first type of conductivity formed in said retention region (8) and a cathode region (12) of the second type of conductivity , said cathode region (12) comprising an epitaxial layer (6) located above said buried anode region (4) and highly doped regions (11) provided at the surface of said epitaxial layer (6) and characterised in that said buried anode region (4) comprises depressions (5) at its interface with said epitaxial layer (6), each of said highly doped regions (11) being located vertically above a corresponding depression (5). Diode in accordance with claim 1 characterised in that said depressions (5) are formed by the intersection of lateral diffusions of distinct and adjacent portions of the buried anode region (4). Diode in accordance with claims land 2 characterised in that the buried anode region (4) has a type P conductivity. Diode in accordance with claims 1, 2and 3 characterised in that the highly doped regions (11) have a type N conductivity. Process of manufacturing a diode according to claim 1 characterised in that it comprises: a first masking to provide by implantation the buried anode region (4) and said implantation being concentrated in distinct and regularly spaced portions, subsequent diffusions in such a manner that the buried anode region (4) takes on a configuration comprising depressions (5) formed by the intersection of lateral diffusions of distinct and adjacent portions, and a second masking for implantation of each of the highly doped regions (11) vertically above a corresponding depression (5) .

Inventors: GALBIATI PAOLA, MASTROMATTEO UBALDO, GALBIATI, PAOLA, MASTROMATTEO, UBALDO
Applicants: ST MICROELECTRONICS SRL, STMICROELECTRONICS S.R.L.
Application year: 1994
Main classification: H01L29
IPC codes: H01L21, H01L29